Method of controlling plant transpiration



United States Patent 3,539,373 METHOD OF CONTROLLING PLANT TRANSPIRATION Anson R. Cooke, Horsham, Pa., assignor to Amchem Products, Inc., Ambler, Pa., a corporation of Delaware No Drawing. Filed June 26, 1967, Ser. No. 649,036

Int. Cl. A01n 5/00 US. Cl. 117-3 Claims ABSTRACT OF THE DISCLOSURE The method of controlling plant transpiration involving use of prepolymers comprising the reaction product of a polyisocyanate and a compound having active hydrogen atoms to control plant transpiration, said method comprising applying said reaction product to leaves of plants.

This invention is concerned with processes for the control of plant transpiration.

Plant transpiration is the escape of water vapour to the atmosphere while carbon dioxide and oxygen are being taken in by the plant through the leaf stomates. Ordinarily, the water loss is made up by Water taken in from the soil but where no water is available in the soil or Where the plant lacks an adequate root system to draw on the water, the water loss can cause the plant to wilt and ultimately to die. This is a severe agronomic problem in areas subject to drought, and it is often the cause of the failure of transplanted nursery stock, of the death of plants during severe cold spells (known as Winterkill), and of the denuding of indoor Christmas trees (known as Needledrop).

It has already been proposed to use aqueous emulsions of polyvinyl chloride in relatively high concentration to coat plant leaves to minimize water loss caused by plant transpiration. These coatings, however, give very little reduction in the rate of water loss and they do not allow the plant leaf to continue growth.

It has now been discovered that the application of certain prepolymers to plant leaves reduces transpiration while allowing other metabolic processes, including leaf growth, to continue substantially unimpaired.

The prepolymers with which this invention is concerned are the reaction products of polyisocyanates, generally diisocyanates, present in a molar excess with compounds containing active hydrogen atoms. By molar excess of polyisocyanate is meant an excess of the polyisocyanate over that necessary to react with the active hydrogen atoms of the other ingredient.

The prepolymers are prepared by heating the molar excess of a polyisocyanate and the compound having active hydrogen atoms together, and controlling the free isocyanate content to a low value. Low values are preferred for the purposes of this invention since a high free isocyanate content can cause damage to the plant leaf. Preferably, the free isocyanate content is less than about to dependent on the plant species involved. The free isocyanate content of a prepolymer is determined by reacting a sample thereof with excess n-butylamine in tetrahydrofuran to completion and then determining the excess of the n-butylamine by titration against standard hydrochloric acid solution using a bromphenol blue end point. This method is explained more fully hereinafter.

Appropriate polyisocyanates for use in the formation of the prepolymer include the following:

(1) Alkylene diisocyanates, such as:

ethylene diisocyanate trimethylene diisocyanate pentamethylene diisocyanate ice octamethylene diisocyanate hexamethylene diisocyanate decamethylene diisocyanate propylene 1,2-diis0cyanate butylene 1,2-diisocyanate butylene Lil-diisocyanate (2) Alkylidene diisocyanates, such as:

ethylidene diisocyanate and butylidene diisocyanate (3) Cycloalkylene diisocyanates, such as: cyclopentenylene 1,3-diisocyanate cyclopentenylene, 1,2-diisocyanate cyclohexylene 1,2-diisocyanate cyclohexylene 1,4-diisocyanate (4) Cycloalkylidene diisocyanates, such as:

cyclopentylidene diisocyanate and cyclohexylidene diisocyanate (5) Aromatic diisocyanates, such as:

n-phenylene diisocyanate p-phenylene diisocyanate 2,4-toluene diisocyanate mixtures of 2,4- and 2,6-toluene diisocyanate 3,3'-dimethyl-diphenylmethane-4,4-diisocyanate (6) Aliphatic aromatic diisocyanates, such as:

xylxylene-1,3-diisocyanate xylxylene-1,4-diisocyanate 4,4'-diphenylmethane diisocyanate 4,4-diphenylpropane diisocyanate (7) Derivatives of higher polyisocyanates such as triphenylmethane triisocyanate and polymethylene polyphenyl isocyanate Appropriate compounds having active hydrogen atoms for use in the formation of the prepolymer include those having hydroxyl and carboxyl groups. Examples of suitable compounds include polyesters and polyethers. The polyesters are formed of polycarboxylic acids and alcoholic compounds. Suitable alcoholic compounds for use in the formation of polyesters include:

(1) Diols such as:

ethylene glycol diethylene glycol tetraethylene glycol propylene glycol dipropylene glycol 2-ethyl-1,3-hexanediol 2,2-dimethyl-1,6-hexanediol 1,8-octanediol 1,10-decanediol tetramethyleue glycol 1,2-butanediol 1,3-butanediol 2,3-butanediol 2,2-dimethyl-1,3-propanediol 2,2-diethyl-1,3-propanediol 2-ethyl-2-butyl-1,3-propanediol 2,3-dimethyl-2,3-butanediol 2-methyl-2,4-pentanediol 1,6-hexanediol 2,5-hexanediol (2) Triols including:

glycerine triethanolamine pyrogallol phloroglucinol (3) Monoethers of triols compounds, such as:

glyceryl-alpha-allyl ether glyceryl-alpha-phenyl ether 1,10-decanediol glycerol trimethylol propane 1 ,2,6-hexanetriol glyceryl-alpha-isopropyl ether 5 52 322 cinol (4) Triglycerides, hydroxycontaining unsaturated erythrjtol higher fatty acid usually of castor oil. arabitol (5) Tetrols, for example, erythritol and monoethers pentaerythritgl thereof; xylitol (6) Pentols, such as arabitol, pentaerythritol and xysorbitol litol; dulcitol (7) Hexols such as sorbitol, dulcitol, mannitol and mannitol iditol; h iditol (8) Hydroxy esters sue as an ester prepared from 1 H ydroxy-termrnated polybutadiene may also be used mol i dlbaslc acid a 2 1 a CO1 g i i as the compound to be reacted with the polyisocyanate. p0 i i ep 8 at 5 8 at ram) glyco Preferred prepolymers include those derived from polyor PO yg t e 1 aslcl etweeridz & 2 ester compounds since these exhibit low sensitivity to i a miner ac! f mo 5 ultraviolet light. Specific preferred prepolymers include 2 g s lj p0 5? 5 :5; gi i z the reaction product of poly(ethylene adipate) and 4,4'diy f h T g c f I P 2 z h d phenylmethane diisocyanate; the reaction product of i ar rauoo t s 1 3 p0 yg yco 0 i poly(ethylene adipate) and 2,4-toluene diisocyanate; the 1S beiween an '3 3 aster i are i reaction product of polypropylene glycol diol and mixgf z gg gg gsgggig gg ig g g g g g am tures of 2,4 and 2,6-toluene diisocyanate; and the reac- Suitable dibasic acids and derivatives thereof with which non product of polyp repylene glycol mol and mixtures the aforesaid alcoholic compounds may be condensed inof and 26-m1uene dusccyanate The advantageous control effect on plant transpiration elude of the prepolymers used in the method of this invention adipic acid is shown by the following non-limiting evaluations. azeilic acid succinic acid or its anhydride EVALUATION I glutaric acid or its anhydride The effect on plant transpiration of the prepolymers phthalic acid or its anhydride used in the method of this invention in comparison with terephthalic acid the known polyvinyl chloride emulsion was determined 1,12-dodecanedioic acid using lettuce plants (Latuca sativa, Grand Rapids Vasebacic acid riety), which were chosen because of their large leaf dimers of unsaturated higher fatty acids such as dilinoleic Surface area and high Stomate Contentid Groups each of two lettuce plants, as uniform as possible, were grown in vermiculite and nutrient solution in The g i i i f i i g i 40 plastic pots and sprayed with test solutions each of 5 ml. of f u :5 2 y F i PO y .2 a 5% solids solution wt. to vol. The top of each of the pots y me a i o 9: 3 f e i g i was covered with a Styrofoam disc, allowing only the plant i Propy ene 0X1 g i t e p0 y 3 Us a CO 0 stem to come through, to prevent surface evaporation. Afls one or more of t e O owmg' ter a 24 hours period for adjustment, the nutrient solution ethylene glycol was restored to its original volume and the units were propylene glycol weighed and set in a greenhouse for four hours. They were 1,2-butanediol then reweighed and each plant was excised at the base of 1,3-butanediol the stem and weighed. The results are shown in the follow- 1,4-butanediol ing table, expressed in terms of the weight ratio of grams 2,3-butanediol of water transpired per gram of leaf weight. It will be 2,2-dimethyl-l,3-propanediol seen that all the prepolymers gave reductions in transpira- 2-ethyl-2-butyl-1,3-propanediol tion better than that given by the emulsion of polyvinyl 2,3-dimethyl-2,3-butanedio1 chloride and that the best result was given by poly 2-methyl-2,4-pentadiol (ethylene adipate) mixtures of 2,4 and 2,6-toluene diiso- 1,6-hexanediol cyanate in methyl ethyl ketone. This evaluation as well 2,5-hexanediol as others hereinafter was conducted at approximately 80 2-ethyl-1,3-hexanediol F. daytime temperature and F. night temperature at 1,8-octanedio1 about relative humidity.

Solution applied Approx. Ratio by molecular wt. of wt. water Percent tree compound transpired N G oi having to plant prepolymer active wt. (gms. before hydrogen water/gm. Prepolymer 75% in 25% MEK 1 dilution atoms Solvent plant wt.)

Poly (ethylene adipate)l2,4-toluene diisocyanate 3 44 3 50% acetone/50% MEK 1. 82 Polypropylene glycol diol/ZA-toluene diisocyanate 3. 15 800 MEK 2. 13 no. 3.28 1.97 D03? 3.28 2.07 Poly (ethylene adipate)/4,4'-dipheny1methane diisocyanate- 3. 14 1. 8 Emulsion of polyvinyl chloride- 2. 45 Control 2. 73

1 Methyl ethyl ketone. 3 Not calculated.

8 Mixture of 2,4 and 2,6-toluene diisocyanate;

EVALUATION II Using Norway Spruce (Picea abies) as the test plant and applying the prepolymer as a solids solution in a 50:50 mixture of acetone and methyl ethyl ketone, the following results were obtained.

Prepolymer NCO=44.3%) and 2,6-t.d. mixture 33 Poly(ethylene propylene adipate)/2,4-2,6 mixture toluene diisocyanate (free NCO=66.3%) 37 EVALUATION III Freshly cut Canadian Balsam Fir trees (Christmas trees), each 2-3 meters tall and as uniform as possible were sprayed With 800 ml. of a 5% wt. to vol. solution 2 in acetone of poly(ethylene adipate)/2,4-toluene diisocyanate and then kept indoors for about a month. The weight of needles dropped from the trees was compared with the weight of needles dropped from other trees used as controls, and the following results were obtained.

\1 eight of Weight of needles needles dropped dropped by control by treated Dltference, trees, g trees, g. percent Run:

These results show a significant reduction in the rate of needledrop caused by water loss due to transpiration.

EVALUATION IV Grand Rapids lettuce plants in coarse vermiculite-Mag- Amp (a slow release fertilizer) in plastic pots were grown from the seedling stage in a growth chamber at 27 C. day, 16 C. night and 75% relative humidity. All pots were kept saturated With water until ready for treatment. Each plant was then sprayed with 10 ml. of a 5% solid solution (wt. to vol.) in a :50 acetone: methyl ethyl ketone solution and then returned to the growth chamber. Styrofoam discs allowing only the plant stem through were placed in each pot to prevent surface evaporation. A first weight reading was taken 4 hrs. after removing pots from water. A second weight reading was taken 3 /2 hrs. later to determine the water loss. After the second weight was taken, the pots were returned to water overnight. This procedure was followed for 5 days, and each treatment was repeated 5 times.

1 Mixture with 2,6-t0luenctliisocyanate.

The following results were obtained:

Average Average weight weight loss of loss of treated controls, plants, Compound applied percent percent Polypropylene lycol dial/toluene diisocyanate reaction roduet (mol. Wt. 800, percent N CO 3.15) 0 in a 25% MEK 2 solution 5. 48 4. 86 Polypropylene glycol trlol/toluene dlisocyanate (mol. wt. 1,500, percent N CO=3.28) 75% solution in methyl ethyl ketone 4. 76 4. 6 Polypropylene glycol triol/toluene diisooyanate reaction product (mol. wt. 3,000, percent NCO=3.24) 75% solution ln methyl ethyl ketone 4. 76 4. 54 Poly (ethylene adipate)/toluene diisocyanate reaction product (mol. Wt. 1,000, percent NCO 3.05) 75% solution in methyl ethyl ketone 11.03 8.19 Poly (ethylene adipate)/toluene dilsocyanate reaction roduet (mol. wt. 1,000, percent NCO 2.95) 75 0 solution In methyl ethyl ketone 9. 13 6. 5

pounds.

2 Methyl ethyl ketone.

The foregoing evaluations show that representative prepolymers of this invention can be used to treat different types of stomate plant leaves to reduce the water loss caused by plant transpiration and the consequences thereof.

The prepolymers are applied in an organic solvent medium appropriate therefor and which is non-toxic to the plant to be treated. This is advantageously provided by ketones, esters and ethers. Examples are acetone or methyl ethyl ketone or both and also acetonitrile, ethyl acetate, and methylene chloride.

The prepolymers can be used to control plant transpiration from stomata in a Wide range of plants. Generally speaking, stomata are present on one or both plant leaf surfaces although they can be present on the plant stem. The prepolymers will be used to control plant transpiration in evergreens, shrubs, trees, foliage and roses. They can also be of value in avoiding or minimizing the consequences of Winterkill, Summer scald, Needledrop and transplant shock. They can also be used to reduce drying out of corns, bulbs and tubers during storage. They can also be used to reduce the water loss by transpiration of cotton, especially that grown under artificial irrigation.

The prepolymers can be applied in solvent medium to the plant leaves at very low concentrations, say from about 0.001 to about 10% by weight. When the concentration is low, more than one application may be desirable to form the necessary coating While at higher concentration, a single application will sufiice; it is preferred to use a solution having a solids content of the order of 5% by weight. The solutions may be applied by spray, and conveniently dispensed in an aerosol container. The propellant can be one or more of the halogenated hydrocarbons, known as Freons.

While it is not intended that this invention be limited in any way by the following theory, it is believed that the prepolymers link to chemically reactive groups in the leaf cuticular surface so binding to the leaf a coating which is permeable to carbon dioxide and air but impermeable to water. The coating exhibits elasticity enabling the leaf to continue growth without distortion, while controlling the rate of water loss by plant transpiration.

In the examples of formulations of prepolymers according to this invention given below, all parts are parts by weight, the molecular Weight refers to that of the compound having active hydrogen atoms used to form the prepolymer and the percentage of free isocyanate of the prepolymer after dilution was determined by the following procedure.

Accurately weighed duplicate samples each containing 1 to 1.5 g. of the prepolymer were transferred to 250 ml. glass-stoppered Erlenmeyer or iodine flasks each containing ml. of anhydrous inhibited tetrahydrofuran.

Then 25 ml. of 0.1 N n-butylamine solution in the tetrahydrofuran was added with agitation using a pipette. The flasks were then stoppered and left for ten minutes with frequent swirling. Then a 0.12 solution of *bromophenol blue indicator was added and the excess amine was titrated against 0.1 N hydrochloric acid to a yellow endpoint.

The percentage of free isocyanate was then calculated from the expression [BS 0.4202] /W where B=number of ml. of acid required for blank S=number of ml. of acid required for sample W=weight of sample (grams).

Example I Parts Poly (ethylene adipate) toluene diisocyanate reaction product (mol wt.-1000, free isocyanate=3. 14%) 75 Methyl ethyl ketone 25 Example 11 Polypropylene glycol triol/toluene diisocyanate reaction product (mol wt.-1500, free isocyanate =3.14%) 75 Methyl ethyl ketone 25 Example III Poly(ethylene adipate) /diphenylmethane diisocyanate ('mol wt.1000, free isocyanate=3.l4%) 60 Acetone 40 Example IV Poly(ethylene adipate) and toluene diisocyanate reaction product (free isocyanate 1.82.1%) 75 Acetone 12.5 Methyl ethyl ketone 12.5

Example V Poly(ethy1ene adipate) and toluene diisocyanate reaction product (free isocyanate 4-4.3%) 75 Methyl ethyl ketone 25 prising applying to a plant in sufficient amount to reduce transpiration, a prepolymer comprising a reaction product of a polyisocyanate having free isocyanate groups, and an organic compound having active hydrogen atoms which are capable of reacting with said free isocyanate groups to form a polyurethane, said prepolymer being applied in an organic solvent medium and polymerizing under ambient conditions to form a polyurethane coating upon said plant to prevent loss of water by way of plant transpiration.

2. The method of claim 1 wherein said prepolymer has a free isocyanate content ranging from 1.8 to less than 20%.

3. The method of claim 2 wherein said prepolymer is the reaction product of a polyester and a diisocyanate.

4. The method of claim 2 wherein said prepolymer is the reaction product of a polyether and a diisocyanate.

5. The method of claim 2 wherein said prepolymer is applied in a solvent selected from the class of ketones, esters and ethers.

6. The method of claim 5 wherein said prepolymer is applied in a solvent selected from acetone and methyl ethyl ketone.

7. The method of claim 3 wherein said prepolymer is the reaction product of poly(ethylene adipate) and 4,4 diphenylmethane diisocyanate.

8. The method of claim 3 wherein said prepolymer is the reaction product of poly(ethylene adipate) and mixtures of 2,4 and 2,6-toluene diisocyanate.

9. The method of claim 3 wherein said prepolymer is the reaction product of polypropylene glycol diol and mixtures of 2,4 and 2,6-toluene diisocyanate.

10. The method of claim 3 wherein said prepolymer is the reaction product of polypropylene glycol triol and mixtures of 2,4 and 2,6-toluene diisocyanate.

References Cited UNITED STATES PATENTS 2,901,467 8/1959 Croco 117-461 X 3,157,964 11/1964 Ferguson et al 47-2 X 3,399,990 9/1968 Humphrey et al. 1173 X 3,401,133 9/1968 Grace et al. 117161 X FOREIGN PATENTS 623,410 7/ 1961 Canada.

WILLIAM D. MARTIN, Primary Examiner H. J. GW'INNELL, Assistant Examiner US. Cl. X.R. 4758; 117-161 

